Mike, I've always seen the dog kennels as recycled packing crates, pretty rough and ready. Built in sections of 3 and 4 dogs, sometimes the gap between two sections is roofed over for an extra dog. Probably 1/2 inch planks roughly sawn to length, butt jointed (I think that shingled look is just warped planks). Those forward seem rougher than the rest, possibly they used the best material aft?
The 'Bovril' shot probably the best guide to their construction.
Many of the descriptions you read are authors opinions stated as fact, even though there is often evidence to the contrary. Eg. there are contemporary sketches of six oared jolly boats.
Function would have varied depending on the size of the ship and probably the Captains disposition.
And as always, There will be exceptions.
Fincham (ca1820) gives us this description. It's certainly not 100% correct but it's a start.
The principal boats for attending upon ships are: launches, long boats, barges, pinnaces, cutters, yawls, jolly boats, life boats, and gigs or galleys.
The launches, long boats, barges, pinnaces, and yawls, are carvel-built; and cutters, jolly boats, galleys, gigs, and life boats, are clincher-built.
Launches are in general from 34 to 59 feet in length. They are for watering and carrying stores to the ship, and are sometimes armed and equipped for cruising
at short distances; they are mostly fitted to carry one twelve-pounder carronnade, and sometimes fitted with swivel stocks.
Long Boats are seldom or never employed for the use of British ships of war; they are sharper and wider than launches.
Barges are generally 32 and 35 feet in length. These boats are for accommodation, pincipally for carrying flag officers and captains; and are lined and panelled above
the thwarts, all fore and aft, that they may be richly decorated, if required.
Pinnaces are 28 and 32 feet in length. These boats are for similar purposes as the barges, but to carry officers of less rank; they are not therefore fitted up in quite so
neat a style, as they are lined and panelled no farther foward tnan the stern sheets.
Yawls are in length 26, 25, 18, and 16 feet. These boats are for carrying light stores, provision, and passengers, to and from the ship. To the smaller class of ships,they answer all the purposes of a launch.
Cutters, Jolly Boats, Galleys, Gigs, and life Boats are clincher-built, that they may be made as light as possible.
Cutters are in length from 32 to 16 feet; they are used for various purposes that are common to ship's duty, though sometimes 32 foot cutters are supplied to ships instead of a barge,
and used for the same purposes; and sometimes the shorter boats are called and used as jolly boats.
Galleys are from 28 to 36 feet in length; they are used in enterprises and expeditions against the enemy, and against illegal trade.
Gigs are in length from 16 to 27 feet; they are for swift rowing, and are supplied to ships when light boats are required.
Life Boats are from 16 to 22 feet in length; they are for landing in surfs, performing enterprises and boarding ships, and for saving men that fall overboard,
The various tables of scantlings for boats available break down thwarts in to 'main', 'after', 'fore' and 'loose' which might imply that the 'main', 'after' and 'fore' are not loose and most likely have knees.
The transcripts of the Bounty mutineers trial include statements the the knees and bolts for both the launch and large cutter had to be retrieved from the chests of the carpenter and carpenters mate. These chests weren't all that big so perhaps only the knees of the main thwart (or thwarts in larger boats) were removable.
iMustBeCrazy's post in Endurance - OcCre - 1:70 (Dog Kennels) was marked as the answer